linux-kernel - Re: [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic operations

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Date:   Wed, 2 Dec 2020 12:26:40 +0000
From:   Brendan Jackman <jackmanb@...gle.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        open list <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic
 operations

On Tue, Dec 01, 2020 at 06:22:50PM -0800, Andrii Nakryiko wrote:
> On Fri, Nov 27, 2020 at 10:01 AM Brendan Jackman <jackmanb@...gle.com> wrote:
[...]
> > +
> > +static void test_xchg(void)
> > +{
> > +       struct atomics_test *atomics_skel = NULL;
> 
> nit: = NULL is unnecessary
[...[
> > +       CHECK(atomics_skel->data->xchg32_value != 2, "xchg32_value",
> > +             "32bit xchg left unexpected value (got %d want 2)\n",
> > +             atomics_skel->data->xchg32_value);
> > +       CHECK(atomics_skel->bss->xchg32_result != 1, "xchg_result",
> > +             "32bit xchg returned bad result (got %d want 1)\n",
> > +             atomics_skel->bss->xchg32_result);
> 
> ASSERT_EQ() is less verbose.
> 
> > +
> > +cleanup:
> > +       atomics_test__destroy(atomics_skel);
> > +}
> > +
> > +void test_atomics_test(void)
> > +{
> 
> why the gigantic #ifdef/#else block if you could do the check here,
> skip and exit?
> 
> > +       test_add();
> > +       test_sub();
> > +       test_and();
> > +       test_or();
> > +       test_xor();
> > +       test_cmpxchg();
> > +       test_xchg();
> 
> 
> please model these as sub-tests, it will be easier to debug, if anything
> 
> > +}
> > +
> > +#else /* ENABLE_ATOMICS_TESTS */
> > +
> > +void test_atomics_test(void)
> > +{
> > +       printf("%s:SKIP:no ENABLE_ATOMICS_TEST (missing Clang BPF atomics support)",
> > +              __func__);
> > +       test__skip();
> > +}
> > +
> > +#endif /* ENABLE_ATOMICS_TESTS */
> > diff --git a/tools/testing/selftests/bpf/progs/atomics_test.c b/tools/testing/selftests/bpf/progs/atomics_test.c
> > new file mode 100644
> > index 000000000000..3139b00937e5
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/atomics_test.c
> > @@ -0,0 +1,124 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include <linux/bpf.h>
> > +#include <bpf/bpf_helpers.h>
> > +#include <bpf/bpf_tracing.h>
> > +
> > +#ifdef ENABLE_ATOMICS_TESTS
> > +
> > +__u64 add64_value = 1;
> > +__u64 add64_result = 0;
> > +__u32 add32_value = 1;
> > +__u32 add32_result = 0;
> > +__u64 add_stack_value_copy = 0;
> > +__u64 add_stack_result = 0;
> 
> empty line here
> 
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(add, int a)
> > +{
> > +       __u64 add_stack_value = 1;
> > +
> > +       add64_result = __sync_fetch_and_add(&add64_value, 2);
> > +       add32_result = __sync_fetch_and_add(&add32_value, 2);
> > +       add_stack_result = __sync_fetch_and_add(&add_stack_value, 2);
> > +       add_stack_value_copy = add_stack_value;
> > +
> > +       return 0;
> > +}
> > +
> > +__s64 sub64_value = 1;
> > +__s64 sub64_result = 0;
> > +__s32 sub32_value = 1;
> > +__s32 sub32_result = 0;
> > +__s64 sub_stack_value_copy = 0;
> > +__s64 sub_stack_result = 0;
> 
> same
> 
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(sub, int a)
> > +{
> > +       __u64 sub_stack_value = 1;
> > +
> > +       sub64_result = __sync_fetch_and_sub(&sub64_value, 2);
> > +       sub32_result = __sync_fetch_and_sub(&sub32_value, 2);
> > +       sub_stack_result = __sync_fetch_and_sub(&sub_stack_value, 2);
> > +       sub_stack_value_copy = sub_stack_value;
> > +
> > +       return 0;
> > +}
> > +
> > +__u64 and64_value = (0x110ull << 32);
> > +__u64 and64_result = 0;
> > +__u32 and32_value = 0x110;
> > +__u32 and32_result = 0;
> 
> yep
> 
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(and, int a)
> > +{
> > +
> > +       and64_result = __sync_fetch_and_and(&and64_value, 0x011ull << 32);
> > +       and32_result = __sync_fetch_and_and(&and32_value, 0x011);
> > +
> > +       return 0;
> > +}
> > +
> > +__u64 or64_value = (0x110ull << 32);
> > +__u64 or64_result = 0;
> > +__u32 or32_value = 0x110;
> > +__u32 or32_result = 0;
> 
> here too
> 
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(or, int a)
> > +{
> > +       or64_result = __sync_fetch_and_or(&or64_value, 0x011ull << 32);
> > +       or32_result = __sync_fetch_and_or(&or32_value, 0x011);
> > +
> > +       return 0;
> > +}
> > +
> > +__u64 xor64_value = (0x110ull << 32);
> > +__u64 xor64_result = 0;
> > +__u32 xor32_value = 0x110;
> > +__u32 xor32_result = 0;
> 
> you get the idea... How often do you define global variables in
> user-space code right next to the function without an extra line
> between them?..
> 
[...]
> > +       cmpxchg64_result_succeed = __sync_val_compare_and_swap(
> > +               &cmpxchg64_value, 1, 2);
> > +
> > +       cmpxchg32_result_fail = __sync_val_compare_and_swap(
> > +               &cmpxchg32_value, 0, 3);
> > +       cmpxchg32_result_succeed = __sync_val_compare_and_swap(
> > +               &cmpxchg32_value, 1, 2);
> 
> single lines are fine here and much more readable

Thanks, ack to all comments.